1. Technical Field
The present invention relates to imaging technology and more particularly to systems and methods for photon detection for use in integrated circuit analysis.
2. Description of the Related Art
Hot-carrier photon emission from very large scale integration (VLSI) circuits has been employed for localizing and identifying failures in circuits. With the introduction of Emission Microscopy, hot-carrier photon emission soon became an essential instrument for physical failure analysis by localizing hot-spot emission, shorts, non-uniform quiescence/stand-by current of the chip (IDDQ), etc. More advanced extensions have also been added to this technique in recent years, based, for example, on the detection of the Light Emission due to Off-State Leakage Current (LEOSLC): circuit logic states mapping, power grid drop calculation, circuit internal temperature and gate self heating measurements, etc.
In 1995, the concept of Picosecond Imaging for Circuit Analysis (PICA), also called Time-Resolved Emission (TRE), was introduced and used. This technique permits the observation in time of the faint near-infrared (NIR) light pulses emitted by hot carriers during the switching transitions of complementary metal oxide semiconductor (CMOS) transistors. From the optical waveforms, it is possible to extract propagation delays, signal skews and other timing problems in a non-invasive and very effective way. These features dictated the immediate widespread adoption of PICA by the testing and diagnostic community. Emissions can be measured in a static way (integrated in time) or dynamically (timing waveforms).
Nowadays, the continuous trend of the modern semiconductor industry towards smaller devices and lower supply voltages is causing significant changes in the intensity and spectrum shift of the light emitted by present CMOS generation. In particular, the progressive shift of the spectral distribution of emitted light towards longer wavelengths pushed for the development of innovative photodetectors.
Although promising, all prototypes of new imaging photodetectors so far developed have significant disadvantages (such as high noise, hot-spots, non-uniformity, high time jitter) that precluded their adoption for PICA measurements. In fact, manufacturing even single pixel photodetectors with low noise and low jitter is complicated and leads to a very low yield, and high cost. The manufacturing technology does not seem mature enough to yield arrays of such photodetectors to create a performing imaging photodetector.